JPH04333349A - Horizontally continuous casting method - Google Patents

Abstract

PURPOSE:To provide the method for stably casting a cast billet having excellent surface characteristic. CONSTITUTION:In the horizontal continuous casting method intermittently drawing 4, the cast billet from a mold according to a velocity pattern containing the drawing process composed of accelerating stage stationary stage and decelerating stage, by gradually increasing the acceleration from zero at the initial stage in the above accelerating stage and accelerating, it is prevented that excess drawing force is rapidly given to solidified shell and stable casting can be executed without breaking the solidified shell and the cast billet having beautiful surface characteristic can be obtd.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a horizontal continuous casting method,
In particular, it relates to a method for drawing slabs in a horizontal continuous casting method. This invention is utilized for continuous casting of billets of carbon steel, stainless steel, and other metals.

0002

[Prior Art] Horizontal continuous casting equipment has lower equipment costs, installation area, and operating costs than vertical continuous casting equipment.
In addition, there is no stress caused by bending the slab, and the internal pressure of the slab is low, so bulging is less likely to occur. In particular, it is economically efficient for small-capacity casting equipment. Therefore, in recent years, horizontal continuous casting equipment has been put into practical use for casting billets and the like.

[0003] FIG. 4 shows a longitudinal section of the main part of a general horizontal continuous casting apparatus. As shown in the drawings, in the horizontal continuous casting apparatus, a tundish 11 and a mold 18 are in communication via a tundish nozzle 12, a sliding nozzle 13, and a feed nozzle 15. The tundish 11, the tundish nozzle 12, the sliding nozzle 13, and the feed nozzle 15 are each made of a normal refractory such as zircon or alumina. The mold 18 is made of copper and is cooled by cooling water W flowing through a cooling water flow path 19. A break ring 16 is attached to the entrance side of the mold 18. The break ring 16 is made of heat-resistant ceramics such as boron nitride and silicon nitride. The entrance of the mold 18 and the break ring 16 are tapered, and when the tundish 11 and the mold 18 are connected, the break length 16 is press-fitted into the mold entrance. Due to the wedge action, surface pressure is generated on the joint surfaces of the mold 18 and the break length 16 to maintain a seal between them. Note that the mold 21 placed next to the copper mold 18 is made of graphite. Furthermore, some devices are not equipped with the sliding nozzle 13.

[0004] The molten metal M supplied into the mold 18 is cooled by the inner peripheral surface of the mold and forms a solidified shell S. Formation of the solidified shell S starts from the break ring 16. The break ring 16 prevents the solidified shell S from growing in the opposite direction, that is, toward the feed nozzle 15 side. A slab K formed by solidifying the molten metal M is intermittently pulled out from the exit side of the mold 18 by a pulling device 25 equipped with pinch rolls 26. When slab K is pulled out intermittently, break length 1
A gap is created between 6 and the end of the solidified shell S, and a new molten metal M flows into the gap to generate a new solidified shell S.

[0005] The above-mentioned drawing of the slab is performed periodically by repeating a certain speed pattern. The speed pattern includes patterns such as pulling out + stopping, pulling out + pushing back, pulling out + stopping + pushing back, or pulling out + stopping + pushing back + stopping. By temporarily stopping the drawing of slabs,
The solidified shell in contact with the break ring grows to a strength that will not break due to the pulling force. Furthermore, by pushing back the slab to compensate for the solidification shrinkage of the solidified shell, breakage of the solidified shell can be prevented, and the surface properties of the slab are improved. An appropriate speed pattern is selected depending on casting conditions, product size, material, etc.

[0006] These speed patterns are well known and are disclosed, for example, in Japanese Patent Application Laid-open No. 57-177868 or Japanese Patent Application Laid-Open No. 61-46364.

[0007]

[Problem to be solved by the invention] Conventional slab drawing
As is clear from the speed pattern illustrated in the above publication, the speed is increased from 0 to a predetermined pulling speed at a constant acceleration in the acceleration stage of the drawing stroke. In other words, the acceleration reaches the predetermined acceleration from 0 all at once. Therefore, the solidified shell is rapidly pulled out during the acceleration stage, and excessive tensile stress is applied to the solidified shell. As a result, cracks (hot tear) occur in the final solidified portion, and furthermore, the solidified shell itself breaks, causing defects on the surface of the slab, and the surface quality of the slab significantly deteriorates. Furthermore, if the solidified shell breaks and breakout occurs, the casting operation must be interrupted, making it impossible to perform the casting operation stably.

[0008] Therefore, the present invention aims to provide a horizontal continuous casting method for stably casting slabs with excellent surface properties.

[0009]

[Means for Solving the Problems] The horizontal continuous casting method of the present invention is a horizontal continuous casting method in which a slab is intermittently pulled out from a mold according to a speed pattern including a pulling stroke consisting of an acceleration stage, a constant speed stage, and a deceleration stage. , the acceleration is gradually increased from 0 at the beginning of the acceleration stage. That is, taking time t in the horizontal axis direction and drawing speed V in the vertical axis direction, the speed curve in the acceleration stage is expressed as a continuous function of time t by the following formula (1) V=f(t) (t≧0)
…
In the case shown in (1), it means that both f(t) and the differential function of the same function with respect to t, f'(t)=df(t)/dt, are 0 at t=0. . When the above conditions are expressed as equations, the following equations (2) and (3) are obtained. f(0)=0

...(2) f'(0)=0

...(3) As an example, the function f(
Suppose that t) is expressed by the following equation (4). V=f(t)=k・tm (t≧0,
k>0, m>0) ...(4) Here, f'(t)
is the time differential of velocity, that is, acceleration, and if this is set as α, then the differential function α=f′(t) with respect to t in equation (4) is expressed by equation (5) below. α=f′(t)=k・m・tm−1
…(5
) At this time, the condition for the acceleration α to gradually increase from 0 is m
> 1, and if this condition is satisfied, the solidified shell will not be pulled out rapidly at the beginning of the acceleration stage, so no excessive tensile stress will be applied to the solidified shell, and the acceleration will be linear or curved. gradually increases from 0.

For example, the value of m is i) m=0.5, i
For the three cases i) m=1, iii) m=2,
The functional forms of velocity V and acceleration α are shown in FIGS. 1 and 2, respectively. Among these three types, the acceleration gradually increases from 0 only when m=2.

The speed pattern to which this invention is applied is not particularly limited. For example, pull + stop, pull + push back, pull + stop + push back, or pull + stop +
It can be applied to any pattern of pushing back and stopping.

0012

[Operation] Since the acceleration gradually increases from 0 at the beginning of the acceleration stage, no sudden excessive pulling force is applied to the solidified shell. As a result, the solidified shell will not break due to the pulling force.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows an example of the slab drawing speed and acceleration pattern according to the present invention. In the figure, accelerations a to g correspond to velocities A to G. The speed pattern consists of pull-out strokes A, B, C, and D, a first stop stroke E, a push-back stroke F, and a second stop stroke G. At the beginning of the drawing stroke, the acceleration is increased along curve a until the acceleration reaches 1.0 m/sec2. Thereafter, the speed is increased at a constant acceleration (B) until the drawing speed reaches 100 mm/sec, and the constant speed is maintained for 50 msec (C). Subsequently, the slab is pushed back (F) through deceleration (D) and a first stop stroke (E). Furthermore, one cycle of slab drawing is completed through a first stop stroke (G) of 150 msec. The period of one cycle is 500 msec.

[0014] The slab was intermittently drawn according to the above speed pattern, and a stainless steel billet of 150 mm square was continuously cast. As a result, the solidified shell did not break during casting, and stable casting was possible. Moreover, there were no casting defects such as cracks, and a slab with beautiful surface texture could be obtained.

[0015]

According to this effect, since the acceleration is gradually increased from 0 at the beginning of the acceleration stage, no sudden excessive pulling force is applied to the solidified shell. As a result, a slab with excellent surface properties can be obtained, and the solidified shell will not break due to the pulling force, allowing stable casting work.

[Brief explanation of drawings]

[Figure 1] The velocity V in the acceleration stage is expressed as a function V=f(t)=k・t
This is an example of a function curve when m is set.

FIG. 2 is a diagram showing an example of an acceleration curve.

FIG. 3 is a diagram showing an example of the speed and acceleration pattern of slab drawing according to the present invention.

FIG. 4 is a longitudinal sectional view showing an example of an apparatus for carrying out the present invention.

[Explanation of symbols]

11 Tundish
25 Pulling device 12 Tundish nozzle
28 Pinch roll 13 Sliding nozzle
K Slab 15 Feed nozzle
M Molten metal 16
break ring
S Solidified shell 18 Copper mold
W Cooling water 21 Graphite mold

Claims (1)

[Claims] 1. A horizontal continuous casting method in which a slab is intermittently pulled out of a mold according to a speed pattern including a pulling stroke consisting of an acceleration stage, a constant speed stage, and a deceleration stage, in which the acceleration is gradually reduced from 0 at the beginning of the acceleration stage. Horizontal continuous casting method characterized by increasing acceleration.